1. Field of the Invention
The present invention relates to a two-pack type curable resin composition used for adhesive, sealing agent, etc. In particular, the present invention relates to a two-pack type curable resin composition capable of securing a sufficient working life and having excellent curing property.
2. Description of the Related Art
The polyisocyanate compound forms a three-dimensional cross-linked structure through a reaction with a curing agent such as amine to thereby provide a polyurethane cured product that is high in strength, elongation, abrasion resistance, and grease resistance. Therefore, the polyisocyanate compound is used as a main ingredient for a joint compound, sealant, adhesive, etc.
An isocyanate group of the polyisocyanate compound generally has high reactivity, and if it is mixed with a curing agent such as amine, the compound reacts therewith immediately. Thus, the mixture (composition) of the polyisocyanate compound and the curing agent gelates or cures before use, causing a serious problem in practical use.
As techniques to solve the problem, there are proposed various compositions such as one-pack type composition and two-pack type composition employing amines having low reactivity or potential curing agents generating amine and the like under certain conditions (see, e.g., JP 10-183058 A and JP 9-169829 A).
For example, a two-pack type curable resin composition including the potential curing agent and a main agent containing a resin ingredient such as urethane prepolymer (polyisocyanate compound) solves the problem on gelation or curing to some extent due to the characteristics of the potential curing agent.
The composition obtained after mixing the curing agent and the main agent, however, has the same formulation as that of a one-pack composition containing the curing agent and the main agent after all, and is also cured by the same curing method as the method of curing the one-pack composition. Thus, the two-pack type composition described above has a similar problem as that on the one-pack composition. That is, in the case of the two-pack type composition, the curing reaction generally starts from the composition surface that contacts with moisture similar to the case of the one-pack composition. Thus, while the surface of the composition shows excellent curing property, the curing reaction in the deep (inner) portion of the composition, which does not contact with moisture is unlikely to occur, resulting in a problem of poor curing property (see, e.g., JP 11-322894 A).
Alternately, there is known a method in which an epoxy resin is incorporated into a resin ingredient of a main agent for the purpose of increasing mechanical characteristics (tensile strength, breaking strength, breaking elongation, etc.), adhesive property, etc. of a composition and a cured product. In the case of using a ketimine compound which is activated by moisture as a curing agent in the method, a similar problem as above occurs likewise (see, e.g., JP 2002-37841 A)
As explained above, in a two-pack type urethane-based curable resin composition including a first liquid containing a resin ingredient and a second liquid containing a curing agent, securing a time during which the composition is allowed to be used without gelation or curing after mixing the first liquid and the second liquid (when used as an adhesive, the time means a time period during which the composition is available for sticking after preparation, and the time is referred herein to as “working life”) and acquiring excellent curing property (particularly, deep curing property) have contrary characteristics respectively, and there has not been known a curable resin composition satisfying both of these characteristics in a high level.